Thin and short communication devices are becoming more popular. Communication systems have to be designed within a limited amount of spaces. For example, a communication system with a plurality of antennas has to be designed in a small space. However, when two antennas are designed in the same small space, interference between the two antennas would be huge if isolation between the two antennas is not sufficient. Thus, signal transmission is affected and transmission rate may be reduced as well. Moreover, it is easy to generate current interference near an edge of the ground when two antennas are disposed in two sides of the ground. Improvement in the art is preferred.